In European Patent EP 0 263 928 B1, stainless steel membranes serving as vacuum and heat isolation elements are described. These heat isolation elements are as a rule plate-shaped metallic vacuum shells whose edges may form undesirable hat-transmission bridges between the bottom sheet and the top sheet. To minimize the losses from such thermally conductive bridges, the wall thickness of the envelope is reduced in these regions and the connection between the bottom sheet and the top or cover sheet can be increased by providing between the edges membranes with bellows-like shapes.
To maintain the vacuum along the edges of the sheets, the stainless steel membrane is provided as a stainless steel metal strip whose ends are welded together into a continuous ring.
The formation of a membrane with a bellows like pattern in the form of a ring or endless band of this type, for the aforedescribed purpose, has been found to be problematical since the requisite precision could not be achieved by earlier techniques.
For example, if the strip is shaped in a roll press it is not possible to ensure that the edge regions will be completely flat and homogeneous without defects where the strip is to be connected to the sheets of the heat insulation element.